The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
Free tracker included with every download this week
Pregnancy and Mounjaro: What You Need to Know
Mounjaro (tirzepatide) is not recommended during pregnancy, and women who are pregnant or planning to become pregnant should not use this medication. If you're considering weight management with tirzepatide or another GLP-1 medication, it's essential to discuss pregnancy plans with your GP or prescriber. This guide explains the current guidance, why Mounjaro is not suitable during pregnancy, and what alternatives may be available for women managing their weight around pregnancy.
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Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
Why Mounjaro Is Not Recommended in Pregnancy
Mounjaro (tirzepatide) is contraindicated in pregnancy because there is insufficient safety data in pregnant women. The medication has not been adequately studied in human pregnancy, and animal studies have shown potential risks to fetal development. For this reason, Mounjaro is not prescribed to women who are pregnant or breastfeeding.
Additionally, Mounjaro may affect the absorption of oral contraceptives. Women taking oral contraceptives who start Mounjaro should add a barrier method or switch to a non-oral contraceptive for 4 weeks after starting treatment and for 4 weeks after each dose increase, as recommended in the UK prescribing information.
If you are taking Mounjaro and discover you are pregnant, contact your GP or prescriber immediately. Do not continue taking the medication without medical guidance.
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How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Planning Pregnancy: What You Should Do
If you are currently taking Mounjaro and are planning to become pregnant, discuss this with your GP or the prescriber who manages your tirzepatide treatment. They will advise when to stop the medication before attempting to conceive. Most guidance suggests discontinuing GLP-1 and GIP/GLP-1 medications several weeks before trying to become pregnant.
During pregnancy, weight management should focus on healthy eating and gentle physical activity rather than medications. Your GP and midwife will provide personalised guidance on safe weight gain during pregnancy and postpartum weight management. After pregnancy and if you are not breastfeeding, you may be able to restart weight management medications under medical supervision.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Is Mounjaro safe during pregnancy?
No, Mounjaro is not safe during pregnancy. It has not been adequately studied in pregnant women, and animal studies raised concerns about fetal development. Mounjaro is contraindicated in pregnancy, meaning it should not be prescribed to or used by pregnant women. Always inform your prescriber if you are pregnant or planning to become pregnant.
What should I do if I become pregnant while taking Mounjaro?
If you discover you are pregnant while taking Mounjaro, contact your GP or prescriber immediately. Do not continue taking the medication without medical guidance. Your GP will advise you on next steps. Early notification is important to ensure the safety of you and your baby.
Can I take Mounjaro while breastfeeding?
Mounjaro is not recommended during breastfeeding. It is not known whether tirzepatide passes into breast milk, and there is insufficient safety data. Discuss breastfeeding plans with your prescriber. Weight management medications are typically reintroduced only after breastfeeding has stopped.
When can I restart Mounjaro after pregnancy?
You can discuss restarting Mounjaro with your GP after pregnancy, ideally once you have finished breastfeeding. Your prescriber will assess your individual health and weight management needs. A clinical assessment will be required before restarting any prescription weight loss medication.
What are the alternatives for weight management during pregnancy?
During pregnancy, focus on healthy eating patterns, appropriate weight gain, and gentle physical activity as recommended by your midwife. After pregnancy, your GP can discuss weight management options including lifestyle changes and, if appropriate, prescription medications after breastfeeding has stopped.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.